Minimizing vehicle engine emissions is desirable to reduce environmental impacts as well as to comply with governmental mandates, such as regulations promulgated by the United States Environmental Protection Agency (EPA).
In a typical after-treatment architecture, the engine exhaust is sent through a three way converter (TWC), after which it passes through a lean NOx trap (LNT) before leaving through an exhaust pipe. The LNT stores NOx during lean engine operations and, when LNT storage capacity is reached, the stored NOx is reduced by rich tip-ins (rich operation). NOx will slip or breakthrough during the transition from lean to rich engine operation and this slip amounts to significant exhaust pipe emissions. Thus, there is a need to reduce LNT NOx breakthrough.